Hinged assembly and dismantling systems for firearms are usually only found on break-open shotguns and rifles, and not on smaller types of firearms, such as pistols. The usual manufacturing technique for production of a firearm that employs a hinged assembly and dismantling system requires the use of components which must be produced extremely precisely. This also necessitates the use of hand fitting. Both techniques are costly and difficult to produce. Hinged assembly and dismantling systems also have inherent problems when employed in mass-produced firearms of any type. The problem is the ability to fit all the components together with a level of precision that would allow for smooth and easy operation, while at the same time enabling a tight and solid lockup free of any play or motion between the components.
Firearm manufacturers are beginning to employ hinged assembly and dismantling systems in smaller firearms, such as the Ruger MK-IV .22 caliber pistol manufactured by Sturm, Ruger & Co., Inc. (“Ruger”). The hinged assembly and dismantling system utilized in the Ruger MK-IV pistol is described in U.S. Pat. No. 9,791,223 (“the '223 patent”), the disclosure of which is incorporated herein by reference thereto. FIGS. 1-4 herein are illustrations of a firearm 10 showing the hinge assembly and dismantling system. FIG. 1 shows the firearm 10 in an open or removal position of an assembled state with a receiver 12 having a mid-portion 14 that is operatively connected to a forward portion 16 of a frame 18 by a hinge 20, which permits the mid-portion 14 of the receiver 12 to rotate about the hinge 20 relative to the frame 18 such that the receiver 12 can be rotated from a closed or operational position where a rear portion 22 of the receiver 12 is substantially parallel to and connects with the frame 18 to the removal position (or open position) where the rear portion 22 of the receiver is separated from the frame 18, as shown in FIG. 1, to permit removal of the receiver 12 from the frame. FIG. 2 shows the firearm 10 with the receiver 12 dismantled or removed from the frame 18.
Referring to FIGS. 3-4, to minimize play and motion between the receiver 12 and the frame 18, a cylindrical rubber plug 24 is installed in a lug hole 26 in the top of a component known as the frame lug 28, which is removably mounted in a recess or channel 30 in the frame 18 at the forward portion 16 of the frame 18 such that it forms a part of the hinge 20. Upon hinging the receiver 12 and the frame 18 and moving the receiver 12 into the closed or operational position, the rubber plug 24 is compressed by a bottom surface of the receiver 12 against the frame lug 28 to provide a snug fit between the receiver 12 and the frame 18. The frame lug 28 and rubber plug 24 are shown and described in the '223 patent, respectively, as elements 450 (separate frame pivot insert) and 340 (resiliently compressible rubber or elastomeric bumper) at column 21, lines 62 to column 23, line 31 and FIGS. 46, 47 and 51-55.
However, when using a rubber plug 24 of the type disclosed in the '223 patent, there remains undesirable play or motion between the receiver 12 and the frame 18. The rubber plug 24 will also deteriorate through normal wear and the play or motion between the receiver 12 and frame 18 will become greater over time. The rubber plug 24 will also not provide a consistent level of pressure to achieve a snug fit between the receiver 12 and frame 18, which will allow for additional play or motion between these components. Once the play or motion between the receiver 12 and frame 18 becomes greater, the wear on these components will be accelerated, necessitating repair or replacement. This arrangement is not conducive to a firearm which is expected to provide a long service life.